The present invention is directed to a novel polymer blend for use as a binder in coating compositions.
Various polymers, such as chlorinated or chlorosulfonated polyethylene, have been dissolved in solvents and mixed with conventional fillers and pigments to make coating compositions. The coating compositions must contain sufficient solids to provide adequate covering characteristics and, perhaps even more importantly, the coating when applied as a film to a substrate must be strong and capable of withstanding impact without cracking. In addition, it is often important that the coating compositions have a viscosity low enough to be readily sprayable. It is, however, also desirable to minimize the quantity of solvent for the polymer used in the coating composition in order to improve the efficiency of film build-up, and also for environmental considerations. Coating compositions containing high molecular weight polymers are known to provide better protection against impact and abrasion and have higher strength than coating compositions containing lower molecular weight polymers. However, such compositions necessarily have low solids content and they are difficult to apply on a substrate because the high molecular weight polymers result in high solution viscosities. On the other hand, employing polymers having lower molecular weights usually results in lower viscosity coating solutions, but film strength is inadequate for many uses. This invention provides a binder for coating compositions either clear or containing color pigments, especially useful for marine and industrial maintenance applications and traffic paint applications, that when mixed with one or more organic solvents and, optionally pigments and/or fillers can be readily applied to a substrate. At the same time, the coating compositions have excellent dry film properties. The compositions exhibit non-Newtonian flow behavior, i.e., the films exhibit a rapid decrease in their apparent viscosities with increasing shear. This property enables the coating compositions to have high solids content while, at the same time, they are sprayable by conventional procedures. The coating compositions have minimum solvent emission and good adhesion to the substrate on which they are applied, such as steel panels. A primary object of this invention is to provide a binder that can be used in coating compositions that have excellent tensile strength, resistance to acids, bases and solvent and that exhibit chip and impact resistance.